WCP6894

[1]

Waldron Edge, Duppas Hill, Croydon

Jan^y 20th 1879

Dear Sir

Many thanks for your letter & paper. I must apologise for my last letter in "Nature" wh[ich] I am afraid was a little rude. I want however to get at some proof, or clear explanation of the shrinkage of the interior of earth, to such an extant & within such limits of time [illeg.] account for our existing mountains. I rather think from a passage in [illeg.] (p.220-221) that the law of exchanges will apply to conduction as well as to radiation. I think see now my error in supposing that the interior could not go on cooling faster than the crust, [illeg.] from not considering that ^as the crust approached its lowest degree of temperature possible it would remain at a nearly stationary temp. owing to the heat received by conduction from the interior, being nearly equal to that radiated by the exterior surface.

I am sorry I am not mathematician enough to follow your paper,— but if I understand its [2] main ideas, it goes on the principle of taking the whole amount of contraction since the solidification of the crust. But our existing mountains are all or almost all tertiary, or at least have been almost wholly elevated during tertiary times. Now as it ^is almost certain that the higher temperature of those times was due to external causes, would not the loss of internal heat have been then less, rather greater than now? And as Fourier is stated to have calculated that the loss of internal heat by radiation, at present rate, loss will exceed 1/30,000° in a century = 1 degree in 3 million years, could the amount of contraction due to such an amount of cooling have any effect in producing mountain ranges? It seems to me that, as all the ancient mountains of the globe have long since disappeared, or nearly so, by denudation, and as all our present great mountain ranges are comparatively modern; [3] and further, as so far back as the Carboniferous Period, there is no proof or even real indication of internal heat making itself felt more than now,— taking all these things into consideration is not the contraction of the earth in its earlier stages, quite beside the question as regards our existing mountains?

The more I think and read of geological and organic changes the more impossible I find it to accept Mr. Thomson's calculations as to the limits of geological time, and the more I agree with the remark quoted with approval in your paper, p.18. foot note. It seems to me that the comparatively low density of the earth demonstrates that it cannot be solid rocks to centre, but that it must contain either vast gaseous spaces or a centre of liquefied gases;— & if so all calculations as to their effects in producing upheavals & other phenomena must be impossible owing to our complete ignorance of the conditions of the problem. [4]

This is a subject on which I am very ignorant,— but I feel so strongly that the theory of contractions, & consequent crumpling & falling in of the crust, does not meet all the difficulties of the problem of the recent elevation of our mountain areas, that I am always interested in any attempt to deal with the question,— though I have as yet found none that is to me satisfactory.

With many thanks | Believe me | Yours very faithfully | Alfred R. Wallace [signature]

Revd O. Fisher

P.S. I have made some remarks on the extreme antiquity of life in the earth at the conclusion of the art. "Distribution" in Enc. Brit. p.285

A.R.W.